Six killed in Russia bus bombing
A female suicide bomber has blown herself up on a city bus in southern Russia, killing six people and injuring about 30, officials said.
The attack in Volgograd added to security fears ahead of the Winter Olympics in Sochi.
The suspected bomber was from the North Caucasus, a region in southern Russia where an Islamic insurgency has been simmering for more than a decade following two separatist wars in Chechnya.
A local official said the suspected attacker was married to an Islamic militant.
Volgograd is 400 miles north east of the North Caucasus, while Sochi sits to the west along the Black Sea.
No one immediately claimed the suicide bombing, but it was the first outside the North Caucasus since Chechen rebel leader Doku Umarov three months ago called for a resumption of attacks on civilians and urged militants to target the Sochi Games.
Russia in past years has seen a series of terror attacks on buses, planes and other forms of transportation, some of them carried out by suicide bombers. The last suicide attack on a bus was in 2008.
Twin bombings on the Moscow subway in March 2010 carried out by female suicide bombers killed 40 people and wounded more than 120. In January 2011, a male suicide bomber struck Moscow's Domodedovo Airport, killing 37 people and injuring more than 180.
Umarov, who had claimed the 2010 and 2011 bombings, ordered a halt to attacks on civilian targets because of the mass street protests against president Vladimir Putin in the winter of 2011-12. He reversed that order in July.
The suspected bomber was from Dagestan, one of the predominantly Muslim republics in the North Caucasus, said Vladimir Markin, the spokesman for the Investigative Committee, Russia's main investigative agency.
In a statement, he identified the suspect as 30-year-old Naida Asiyalova. Russian state television showed pictures of Asiyalova's passport.
In Dagestan, the centre of the insurgency, bombings and shootings occur almost daily. Most of them target law enforcement officers, not civilians. The Tsarnaev brothers, accused of carrying out the Boston Marathon bombings, have roots in Dagestan and Chechnya.
Rasul Temirbekov, a spokesman for the Investigative Committee's branch in Dagestan, said the suspected bomber was married to an ethnic Russian, Dmitry Sokolov, whom she met while both were university students in Moscow.
She encouraged him to become a rebel, and he quickly gained a reputation as an expert in explosives, Mr Temirbekov said. Sokolov, also known as Abdull Jabbar, has been on the run.
Mr Temirbekov said the suspected suicide bomber had a fatal bone disease.